This invention is directed to a method of and an apparatus for analyzing the appearance features of a surface. In particular, the invention is directed to detecting the visual characteristics of a surface including orange peel, microwrinkle, cracks and crazes, distinctness of image, gloss, haze, contrast, luster, fog and texture.
Surface appearance is an essential ingredient in marketing manufactured finished products, such as paper, plastics, films, fabrics, finishes, and automobiles. For example, customers generally perceive the degree of perfection in an automotive surface finish to be indicative of the vehicle,s quality. As another example, the perception of gloss or sheen uniformity is indicative of film quality.
Various methods and devices for determining the surface characteristics have been devised in the art, and examples of same are disclosed in U.S. Pat. Nos. 2,975,285; 3,938,892; 4,299,497; 4,527,898; 4,547,073; 4,682,041; 4,717,259; 4,718,760; 4,792,232; and 4,846,578; and U.S. Statutory Invention Registration H220, published Feb. 3, 1987. Various other techniques relating to determining the characteristics of a sample surface are disclosed in the following references:
M. Morita and T. Nakajima, "Design Consideration of a New Instrument for Determining Image Clarity of Coatings", Proc. Xth Internat. Conf. in Organic Coatings Science and Technology, Athens, pp. 199-215 (1984).
M. Matsuta and T. Kubota, "Gloss Measurement on Painted Surfaces", Japanese Journal of Applied Physics, 20, pp. 1145-1152, (June 1981).
M. Matsuta, K. Kito, T. Kubota, "New Portable Orange Peel Meter for Paint Coatings", Williamsburg Conference Proceedings, pp. 25-28, Inter-Society Color Council, Williamsburg, Va., (1987).
M. Matsuta and K. Kito, "Development of a Gloss Tester for Paint Coatings", Japanese Journal of Applied Physics, 21.1, pp. 133-136 (January 1982).
Dr. Donald W. Boyd, "Computerized Roughness/Profile Measurements Quantity Aspects of Appearance:, Proceedings of XIIIth International Conference in Organic Coatings Science and Technology, U.S.A., pp. 59-77, (1987).
"Appearance of Metallic Surfaces", ASTM Special Technical Publication 478, 71st Annual Meeting ASTM, San Francisco, Calif., (Jun. 23-28, 1968).
Various descriptors for characterizing surface appearance attributes have been standardized by the American Society of Testing and Materials (ASTM) and include such terms as orange peel (OP), distinctness of image (DOI), gloss, contrast, crazes, naze anc fog. This is not an exhaustive list since other attributes such as microwrinkle, cracks, and surface imperfections/flaws known in the trade are also descriptive of painted surfaces. In his book, "The Measurement of Appearance", John Wiley, New York (12975), R. Hunter discusses measurement techniques for several of these attributes and stresses that the human psychophysical response to appearance is based on an interplay between measures of color and spatial vision.
In spite of the variety of instrumental methods available to us today to purportedly measure surface appearance parameters, these methods have all fallen short in their ability to fully characterize surfaces, primarily because measurements have been referenced to the surface under test rather than to the visual reference frame of the observer. Consequently, the issue of visualized detail has remained untreated. Typical of instrumentation currently in use is the non-imaging goniophotometer for measuring gloss and haze as a function of reflectance of non-collimated light at prescribed angles around the specular angle with a photocell detector.
Accordingly, the primary purpose of this invention is to provide a method and an apparatus for measuring the visual appearance attributes of surfaces that takes into account the psychophysical response of the spatial visual system, where spatial vision implies a visual capacity to detect and process image highlights, textures, and detail.